A variable intake system is a type of intake manifold technique of an internal combustion engine of a vehicle, which is able to enhance fuel efficiency by varying a length of an intake tract to optimize torque and power according to a speed range of an engine.
Recently, a variable intake system using a resonance effect has been used in a tuning method for enhancing a six-cylinder engine. However, since a range of revolutions per minute (RPM) of an engine is too narrow to implement a resonance effect, a multi-stage variable structure is widely used to increase the range of RPM.
In order to reduce noise in an intake system of an engine, a resonator, or a noise reducing device, is installed in the middle of an air duct. Here, a Helmholtz resonator or a tubular quarter wave resonator is used as a resonator.
However, installation of the Helmholtz resonator or the tubular quarter wave resonator causes a restriction in an installation space, making it difficult to install the resonator and increasing costs.